Coordination of hydraulic and morphological traits across dominant grasses in eastern Australia

Leaf hydraulic traits characterize plant drought tolerance and responses to climate change. Yet, plant hydraulics are biased towards northern hemisphere woody species. We collected rhizomes of several perennial grass species along a precipitation gradient in eastern Australia and grew them in an experimental pot study to investigate potential trade-offs between drought tolerance and plant morphology. We measured the following leaf hydraulic traits: the leaf water potential (psi(leaf)) at 50% and 88% loss of leaf hydraulic conductance (P50(Kleaf) and P88(Kleaf)), the psi(leaf) at 50% loss of stomatal conductance (P50(gs)), leaf turgor loss point (TLP), leaf dry matter content (LDMC), leaf modulus of elasticity (epsilon), and the slope of the relationship between predawn and midday psi(leaf). We also measured basal area, tiller density, seed head density, root collar diameter, plant height, and aboveground biomass of each individual. As expected, grass species varied widely in leaf-level drought tolerance, with loss of 88% hydraulic conductance occurring at a psi(leaf) ranging from -1.52 to -4.01 MPa. However, all but one species lost leaf turgor, and most reached P50(gs) before this critical threshold. Taller more productive grass species tended to have drought vulnerable leaves characterized by low LDMC and less negative P88(Kleaf). Species with greater tiller production experienced stomatal closure and lost turgor at more negative psi(leaf). Although our sample size was limited, we found no relationships between these species' traits and their climate of origin. Overall, we identified important hydraulic and morphological trade-offs in Australian grasses that were surprisingly similar to those observed for woody plants: (1) xylem of taller species was less drought tolerant and (2) turgor loss occurs and stomatal closure begins before significant loss of K-leaf. These data build upon a small yet growing field of grass hydraulics and may be informative of species responses to further drought intensification in Australia. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

Leaf hydraulic traits play a crucial role in plant drought tolerance and responses to climate change. This study focused on perennial grass species in eastern Australia and investigated the trade-offs between drought tolerance and plant morphology. The results showed that taller and more productive grass species had less drought-tolerant leaves, characterized by low leaf dry matter content and less negative leaf hydraulic conductance. Stomatal closure and turgor loss occurred at more negative leaf water potential in species with greater tiller production. These findings contribute to our understanding of grass hydraulic traits and their responses to drought in Australia.